Ablation catheter assembly having a virtual electrode comprising portholes

ABSTRACT

An ablation catheter having a catheter shaft and a virtual electrode, the virtual electrode comprising portholes through an outer peripheral wall of the catheter shaft and a metal electrode, the catheter being used for treatment of cardiac arrhythmia, for example, atrial fibrillation, by electrically isolating a vessel, such as a pulmonary vein, from a chamber, such as the left atrium. The catheter shaft includes a proximal portion and a distal portion. The distal portion includes an active region, which is either a looped structure transverse to the longitudinal axis of the catheter shaft, or a linear structure that extends parallel to the longitudinal axis of the catheter shaft. During use, the active region is directed into contact with, for example, the wall of a pulmonary vein. Upon energization, the virtual electrode creates a continuous lesion on an inner wall of the pulmonary vein, thereby electrically isolating the pulmonary vein from the left atrium.

BACKGROUND OF THE INVENTION

[0001] a. Field of the Invention

[0002] This invention relates to catheters for the mapping and ablationof human tissue, particularly cardiac tissue. In particular, theinvention relates to an ablation catheter comprising a virtual electrodeat a distal portion of the catheter to ablate tissue, the virtualelectrode using energy emanating from a metal electrode contained withinthe distal portion and conductive fluid medium contacted by the metalelectrode before exiting from the distal portion through a plurality ofportholes.

[0003] b. Background Art

[0004] Catheters have been in use for medical procedures for many years.Catheters can be used for medical procedures to examine, diagnose, andtreat while positioned at a specific location within the body that isotherwise inaccessible without more invasive procedures. During theseprocedures a catheter is inserted into a vessel near the surface of thebody and is guided to a specific location within the body forexamination, diagnosis, and treatment. For example, one procedureutilizes a catheter to convey an electrical stimulus to a selectedlocation within the human body. Another procedure utilizes a catheterwith sensing electrodes to monitor various forms of electrical activityin the human body.

[0005] Catheters are also used increasingly for medical proceduresinvolving the human heart. Typically, the catheter is inserted in anartery or vein in the leg, neck, or arm of the patient and threaded,sometimes with the aid of a guide wire or introducer, through thevessels until a distal tip of the catheter reaches the desired locationfor the medical procedure in the heart.

[0006] A typical human heart includes a right ventricle, a right atrium,a left ventricle, and a left atrium. The right atrium is in fluidcommunication with the superior vena cava and the inferior vena cava.The atrioventricular septum separates the right atrium from the rightventricle. The tricuspid valve contained within the atrioventricularseptum provides communication between the right atrium and the rightventricle.

[0007] In the normal heart, contraction and relaxation of the heartmuscle (myocardium) takes place in an organized fashion aselectro-chemical signals pass sequentially through the myocardium fromthe sinoatrial (SA) node, which comprises a bundle of unique cellsdisposed in the wall of the right atrium, to the atrioventricular (AV)node and then along a well-defined route, which includes theHis-Purkinje system, into the left and right ventricles. The AV nodelies near the ostium of the coronary sinus in the interatrial septum inthe right atrium. Each cell membrane of the SA node has a characteristictendency to leak sodium ions gradually over time such that the cellmembrane periodically breaks down and allows an inflow of sodium ions,thereby causing the SA node cells to depolarize. The SA node cells arein communication with the surrounding atrial muscle cells such that thedepolarization of the SA node cells causes the adjacent atrial musclecells to depolarize. This results in atrial systole, wherein the atriacontract to empty and fill blood into the ventricles. The atrialdepolarization from the SA node is detected by the atrioventricular (AV)node which, in turn, communicates the depolarization impulse into theventricles via the bundle of His and Purkinje fibers following a briefconduction delay. The His-Purkinje system begins at the AV node andfollows along the membranous interatrial septum toward the tricuspidvalve through the atrioventricular septum and into the membranousinterventricular septum. At about the middle of the interventricularseptum, the His-Purkinje system splits into right and left brancheswhich straddle the summit of the muscular part of the interventricularseptum.

[0008] Sometimes abnormal rhythms occur in the heart, which are referredto generally as arrhythmia. For example, a common arrhythmia isWolff-Parkinson-White syndrome (W-P-W). The cause of W-P-W is generallybelieved to be the existence of an anomalous conduction pathway orpathways that connect the atrial muscle tissue directly to theventricular muscle tissue, thus bypassing the normal His-Purkinjesystem. These pathways are usually located in the fibrous tissue thatconnects the atrium and the ventricle. Other abnormal arrhythmiassometimes occur in the atria, which are referred to as atrialarrhythmia. Three of the most common atrial arrhythmia are ectopicatrial tachycardia, atrial fibrillation, and atrial flutter. Atrialfibrillation can result in significant patient discomfort and even deathbecause of a number of associated problems, including the following: anirregular heart rate, which causes patient discomfort and anxiety; lossof synchronous atrioventricular contractions, which compromises cardiachemodynamics, resulting in varying levels of congestive heart failure;and stasis of blood flow, which increases the likelihood ofthromboembolism.

[0009] Efforts to alleviate these problems in the past have includedsignificant usage of pharmacological treatments. While pharmacologicaltreatments are sometimes effective, in some circumstances drug therapyhas had only limited effectiveness and is frequently plagued with sideeffects, such as dizziness, nausea, vision problems, and otherdifficulties.

[0010] An increasingly common medical procedure for the treatment ofcertain types of cardiac arrhythmia is catheter ablation. Duringconventional catheter ablation procedures, an energy source is placed incontact with cardiac tissue to heat the tissue and create a permanentscar or lesion that is electrically inactive or noncontractile. Duringone procedure, the lesions are designed to interrupt existing conductionpathways commonly associated with arrhythmias within the heart. Theparticular area for ablation depends on the type of underlyingarrhythmia. One common ablation procedure treats atrioventricular nodalreentrant tachycardia (AVNRT). Ablation of fast or slow AV nodalpathways is disclosed in Singer, I., et al., “Catheter Ablation forArrhythmias,” Clinical Manual of Electrophysiology, pgs. 421-431 (1993).The use of electrode catheters for ablating specific locations withinthe heart has also been disclosed in, for example, U.S. Pat. Nos.4,641,649, 5,228,442, 5,231,995, 5,263,493, and 5,281,217.

[0011] Another medical procedure using ablation catheters with sheathsto ablate accessory pathways associated with W-P-W utilizing both atransseptal and retrograde approach is discussed in Saul, J. P., et al.,“Catheter Ablation of Accessory Atrioventricular Pathways in YoungPatients: Use of long vascular sheaths, the transseptal approach and aretrograde left posterior parallel approach,” Journal of the AmericanCollege of Cardiology, Vol. 21, no. 3, pgs. 571-583 (1 Mar. 1993). Othercatheter ablation procedures are disclosed in Swartz, J. F.,“Radiofrequency Endocardial Catheter Ablation of AccessoryAtrioventricular Pathway Atrial Insertion Sites,” Circulation, Vol. 87,no. 2, pgs. 487-499 (February 1993).

[0012] Ablation of a specific location within the heart requires theprecise placement of the ablation catheter within the heart. Precisepositioning of the ablation catheter is especially difficult because ofthe physiology of the heart, particularly because the heart continues tobeat throughout the ablation procedures. Commonly, the choice ofplacement of the catheter is determined by a combination ofelectrophysiological guidance and fluoroscopy (placement of the catheterin relation to known features of the heart, which are marked byradiopaque diagnostic catheters that are placed in or at knownanatomical structures, such as the coronary sinus, high right atrium,and the right ventricle).

[0013] Ablation procedures using guiding introducers to guide anablation catheter to a particular location in the heart for treatment ofatrial arrhythmia have been disclosed in, for example, U.S. Pat. Nos.5,427,119, 5,497,774, 5,564,440, 5,575,766, 5,628,316, and 5,640,955.During these procedures, ablation lesions are produced in the heart asan element of the medical procedure.

[0014] The energy necessary to ablate cardiac tissue and create apermanent lesion can be provided from a number of different sources.Originally, direct current was utilized although laser, microwave,ultrasound, and other forms of energy have also been utilized to performablation procedures. Because of problems associated with the use of DCcurrent, however, radiofrequency (RF) has become the preferred source ofenergy for ablation procedures. The use of RF energy for ablation hasbeen disclosed, for example, in U.S. Pat. Nos. 4,945,912, 5,242,441,5,246,438, 5,281,213, 5,281,218, and 5,293,868. The use of RF energywith an ablation catheter contained within a transseptal sheath for thetreatment of W-P-W in the left atrium is disclosed in Swartz, J. F. etal., “Radiofrequency Endocardial Catheter Ablation of AccessoryAtrioventricular Pathway Atrial Insertion Sites,” Circulation, Vol. 87,pgs. 487-499 (1993). See also Tracey, C. N., “Radio Frequency CatheterAblation of Ectopic Atrial Tachycardia Using Paced Activation SequenceMapping,” J. Am. Coll. Cardiol. Vol. 21, pgs. 910-917 (1993).

[0015] In addition to radiofrequency ablation catheters, thermalablation catheters have been disclosed. During thermal ablationprocedures, a heating element, secured to the distal end of a catheter,heats thermally conductive fluid, which fluid then contacts the humantissue to raise its temperature for a sufficient period of time toablate the tissue. A method and device for thermal ablation using heattransfer is disclosed in U.S. Pat. No. 5,433,708. Another thermalablation procedure utilizing a thermal electrode secured to a catheterand located within a balloon with openings in that balloon to permitheated conductive fluid introduced into the balloon from the catheter toescape from the balloon for contact with the tissue to be ablated isdisclosed in U.S. Pat. No. 5,505,730.

[0016] Conventional ablation procedures utilize a single distalelectrode secured to the tip of an ablation catheter. Increasingly,however, cardiac ablation procedures utilize multiple electrodes affixedto the catheter body. These ablation catheters often contain a distaltip electrode and a plurality of ring electrodes as disclosed in, forexample, U.S. Pat. Nos. 4,892,102, 5,228,442, 5,327,905, 5,354,297,5,487,385, and 5,582,609.

[0017] To form linear lesions within the heart using a conventionalablation tip electrode requires the utilization of procedures such as a“drag burn.” The term “linear lesion” as used herein means and elongate,continuous lesion, whether straight or curved, that blocks electricalconduction. During a “drag burn” procedure, while ablating energy issupplied to the tip electrode, the tip electrode is drawn across thetissue to be ablated, producing a line of ablation. Alternatively, aseries of points of ablation are formed in a line created by moving thetip electrode incremental distances across the cardiac tissue. Theeffectiveness of these procedures depends on a number of variablesincluding the position and contact pressure of the tip electrode of theablation catheter against the cardiac tissue, the time that the tipelectrode of the ablation catheter is placed against the tissue, theamount of coagulum that is generated as a result of heat generatedduring the ablation procedure, and other variables associated with abeating heart, especially an erratically beating heart. Unless anuninterrupted track of cardiac tissue is ablated, unablated tissue orincompletely ablated tissue may remain electrically active, permittingthe continuation of the stray circuit that causes the arrhythmia.

[0018] It has been discovered that more efficient ablation may beachieved if a linear lesion of cardiac tissue is formed during a singleablation procedure. The production of linear lesions in the heart by useof an ablation catheter is disclosed in, for example, U.S. Pat. Nos.5,487,385, 5,582,609, and 5,676,662. A specific series of linear lesionsformed in the atria for the treatment of atrial arrhythmia are disclosedin U.S. Pat. No. 5,575,766.

[0019] The ablation catheters commonly used to perform these ablationprocedures produce electrically inactive or noncontractile tissue at aselected location by physical contact of the cardiac tissue with anelectrode of the ablation catheter. Conventional tip electrodes withadjacent ring electrodes cannot perform this type of procedure, however,because of the high amount of energy that is necessary to ablatesufficient tissue to produce a complete linear lesion. Also,conventional ring electrode ablation may leave holes or gaps in alesion, which can provide a doorway through which unwanted circuits cantravel.

[0020] An ablation catheter for use in the heart that contains a pair ofintertwined helical electrodes is disclosed in U.S. Pat. No. 5,334,193.The helically wound electrode is affixed to the surface of the catheterbody over a distance of about eight centimeters from the distal tip ofthe catheter body. Other helical electrodes are disclosed in U.S. Pat.Nos. 4,161,952, 4,776,334, 4,860,769, 4,934,049, 5,047,026, 5,542,928,and WO 95/10319.

[0021] During conventional ablation procedures, the ablating energy isdelivered directly to the cardiac tissue by an electrode on the catheterplaced against the surface of the tissue to raise the temperature of thetissue to be ablated. This rise in tissue temperature also causes a risein the temperature of blood surrounding the electrode, which oftenresults in the formation of coagulum on the electrode, which reduces theefficiency of the ablation electrode.

[0022] To achieve efficient and effective ablation, coagulation of bloodthat is common with conventional ablation catheters should be avoided.This coagulation problem can be especially significant when linearablation lesions or tracks are produced because such linear ablationprocedures conventionally take more time than ablation proceduresablating only a single location.

[0023] In some instances, stray electrical signals find a pathway downthe pulmonary veins and into the left atrium of the heart. In theseinstances, it may be advantageous to produce a circumferential lesion atthe ostium of one or more of the pulmonary veins or within one or moreof the pulmonary veins. Desirably, such a circumferential lesion wouldelectrically isolate a pulmonary vein from the left atrium, completelyblocking stray signals from traveling down the pulmonary vein and intothe left atrium. It is desirable to have a catheter tip for forming suchcircumferential lesions in tissue while avoiding problems with existingdesigns.

SUMMARY OF THE INVENTION

[0024] It is an object of the disclosed invention to provide an improvedablation catheter for forming linear lesions in tissue, including tissuewithin the human heart and the pulmonary veins. This and other objectsare provided by the ablation catheter that is disclosed by the presentinvention.

[0025] The instant invention is a catheter for ablating tissue and, inone form, comprises a catheter shaft and a metal electrode. The metalelectrode may be a platinum flat wire adapted to be connected to an RFgenerator. The catheter shaft has a proximal portion, a distal portion,and at least one lumen that extends from the proximal portion to thedistal portion. The distal portion is adapted to be inserted into a bodycavity having tissue to be ablated and may be straight or curved. Thedistal portion comprises an active region that includes a plurality ofportholes. The first lumen is adapted to carry a conductive fluid mediumfrom the proximal portion to the portholes along the active region ofthe distal portion. In one form of the invention, each of the portholesis sized so that the conductive fluid medium flows evenly from each ofthe portholes. The metal electrode, which is adapted to supply ablationenergy to the conductive fluid medium, is mounted in the first lumen andextends along the active region of the distal portion.

[0026] In another form of the ablation catheter of the instantinvention, the catheter comprises a catheter shaft, a metal electrode,and a shape memory wire. The catheter shaft has a proximal portion, adistal portion, a first lumen that extends from the proximal portion tothe distal portion, and a second lumen. The distal portion comprises atleast one curved portion that is configured to be inserted into a bodycavity having tissue to be ablated. For example, the at least one curvedportion may comprise a circular section designed to fit within apulmonary vein around a longitudinal axis of the pulmonary vein. The atleast one curved portion defines an inner peripheral wall and an outerperipheral wall, wherein the outer peripheral wall has an active regionthat includes a plurality of portholes. The first lumen is adapted tocarry a conductive fluid medium from the proximal portion to theportholes along the active region of the distal portion. The metalelectrode, which is adapted to supply ablation energy to the conductivefluid medium, is mounted in the first lumen and extends along the activeregion of the distal portion. The second lumen extends adjacent to theinner peripheral wall. The shape memory wire is mounted in the secondlumen. The shape memory wire may comprise, for example, an alloy ofnickel and titanium (e.g., NiTi) or a strip of stainless steel.

[0027] In still another form of the present invention, the portholesalong the active region of the distal portion comprise a first porthole,at least one intermediate porthole, and a last porthole. The portholesare circular in cross section, and the relative diameter of theportholes increases in size as one moves distally along the activeregion, from the first porthole to the last porthole. A bridge isdefined between adjacent portholes. Each bridge spans a gap between aproximal leading edge of one porthole and a distal trailing edge of anext adjacent porthole. The relative width of the bridges may decreasein size as one moves distally along the active region from the firstporthole to the last porthole.

[0028] In another form, the ablation catheter described above is combinewith at least one guiding introducer (e.g., an inner guiding introducerand an outer guiding introducer) or a precurved sheath, and at least onehemostatic valve to form a complete ablation catheter assembly fortreatment of cardiac arrhythmia.

[0029] The present invention also includes a method for making acatheter assembly for treating cardiac arrhythmia. In one form, themethod comprises the steps of acquiring a shape memory wire having adesired curvilinear shape; acquiring a catheter shaft having a firstlumen formed therein; inserting the shape memory wire into the firstlumen to form a catheter assembly; heating the catheter shaft until itrelaxes and at least partially conforms to the shape of the shape memorywire; and cooling the catheter assembly. The heating step requiresheating the catheter assembly to a temperature that permits the cathetershaft to deform, but ensuring that the temperature remains lower thanthe temperature used to fix the shape of the shape memory wire.

[0030] The foregoing and other aspects, features, details, utilities,and advantages of the present invention will be apparent from readingthe following description and claims, and from reviewing theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is an isometric view of an ablation catheter assemblyaccording to the present invention.

[0032]FIG. 2 is a fragmentary, isometric view of a distal portion of anablation catheter comprising part of the ablation catheter assemblydepicted in FIG. 1.

[0033]FIG. 3 is a fragmentary view along line 3-3 of FIG. 5 of thedistal portion of the ablation catheter depicted in FIGS. 1 and 2looking down the longitudinal axis of a catheter shaft comprising partof the ablation catheter.

[0034]FIG. 4 is a fragmentary view of the distal portion of the ablationcatheter depicted in FIGS. 1-3, looking perpendicular to thelongitudinal axis of the catheter shaft.

[0035]FIG. 5 is a fragmentary view of the distal portion of the ablationcatheter depicted in FIGS. 1-4, looking perpendicular to thelongitudinal axis of the catheter shaft and perpendicular to thedirection from which FIG. 4 is taken.

[0036]FIG. 6 is a fragmentary view of a distal portion of an ablationcatheter similar to the ablation catheter depicted in FIGS. 1-5, butwherein an active region of the catheter is not curved.

[0037]FIG. 6A is an enlarged, fragmentary view of the circled portion ofFIG. 6.

[0038]FIG. 7 is a fragmentary view taken along line 7-7 of FIG. 5,wherein portions of the ablation catheter wall have been broken away toreveal internal features of the distal portion.

[0039]FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7and clearly shows an electrode in a first lumen and a shape memory wirein a second lumen.

[0040]FIG. 9 depicts an alternative cross-sectional shape for the distalportion of an ablation catheter according to the present invention,wherein a single lumen is present and a separate shape memory wire isnot used.

[0041]FIG. 10 is a view similar to FIG. 5, but depicts an alternateconfiguration for the distal portion of the ablation catheter, whereinthe portholes are arranged in parallel rows.

[0042]FIG. 11 is an isometric view of a heart with portions of the atriaand ventricles broken away to reveal positioning of the ablationcatheter depicted in, for example, FIGS. 1-5 in the left atrium prior toinsertion of the ablation catheter into the left superior pulmonaryvein.

[0043]FIG. 12 is similar to FIG. 11, but depicts the ablation catheterin position within the left superior pulmonary vein.

[0044]FIG. 13 is a fragmentary cross-sectional view of an ablationcatheter according to the present invention and having thecross-sectional configuration depicted in FIG. 8, wherein the electrodeis delivering energy to adjacent tissue.

[0045]FIG. 14 depicts a third alternative configuration of an ablationcatheter according to the present invention, wherein the portholes areconfigured to permit formation of a lesion within the left atrium at theostium of a pulmonary vein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] In general, the instant invention relates to an ablation catheterassembly 10 comprising an ablation catheter 18 having a unique distalportion 12 for ablating tissue 14 using energy emanating from anelectrode 16 contained within the ablation catheter 18. A conductivefluid medium 20 (e.g., hypertonic saline) contacting the electrode 16and the tissue 14 to be ablated comprises a virtual electrode,eliminating the need for direct contact between the electrode 16 and thetissue 14 to be ablated.

[0047]FIG. 1 is an isometric view looking downwardly at an ablationcatheter assembly 10 according to the present invention. In thisembodiment of the catheter assembly 10, an ablation catheter 18comprising a catheter shaft 22 having a proximal portion 24 and a distalportion 12 is used in combination with one or more guiding introducers26, 28 to facilitate formation of lesions on tissue 14, for example,cardiovascular tissue. The catheter shaft 22 may be constructed from anumber of different polymers (e.g., PELLETHANE, polypropylene, orientedpolypropylene, polyethylene, crystallized polyethylene terephthalate,polyethylene terephthalate, polyester, polyvinyl chloride, etc.). Asdepicted in FIG. 1, the ablation catheter 18 may be used in combinationwith an inner guiding introducer 28 and an outer guiding introducer 26.Alternatively, a single guiding introducer may be used or a precurvedtranseptal sheath may be used instead of one or more guidingintroducers. In general, the introducer, introducers, or precurvedsheath are shaped to facilitate placement of the ablation catheter 18 atthe tissue 14 to be ablated. Thus, for example, the introducer or theintroducers or the transeptal sheath make it possible to navigate to theheart 30 and through its complex physiology to reach specific tissue 14to be ablated. When the ablation catheter 18 has a specificconfiguration like the curved configuration depicted in FIGS. 1-5, theshape of the introducers 26, 28, if used, may change somewhat when thedistal portion 12 of the ablation catheter 18 is retracted into theintroducers 26, 28. This effect is accounted for by the present design.Referring more particularly to FIGS. 2-5, further details concerning thefirst embodiment of the ablation catheter 18 according to the presentinvention are described next. The distal portion 12 of the cathetershaft 22 includes a first curved section 34 of catheter shaft, a secondcurved section 36 of catheter shaft, and a third curved section 38 ofcatheter shaft, which together comprise a single unitary component inthis embodiment, but which could comprise separate pieces that have beenjoined together. In this embodiment, the third curved section defines anactive region used to ablate tissue. The catheter shaft 22, which istypically a braided shaft, includes a “straight” section 32 that mayfollow a circuitous path from the location of the distal portion 12 ofthe catheter shaft 22 adjacent to the tissue 14 to be ablated back tothe proximal portion 24 of the catheter shaft 22, which is outside ofthe body containing the tissue 14 to be ablated. The straight section 32is joined to the distal portion 12 by an RF bond. The third curvedsection 38 of catheter shaft includes a plurality of portholes throughwhich conductive fluid medium 20 flows while the ablation catheter 18 isin use.

[0048] The plurality of portholes depicted in FIGS. 2-5 includes aninitial or first porthole 40, a plurality of intermediate portholes 42,and a final or last porthole 44, which are described in more detailbelow. This third curved section 38 of catheter shaft is shaped in acircular, nearly closed “C” configuration, as most clearly shown in FIG.3. The first and second curved sections 34, 36, respectively, tie thestraight section 32 to the third section 38 of catheter shaft, whileplacing the straight section 32 of catheter shaft in a position where alongitudinal axis 46 (see FIGS. 2 and 3) extending through the straightsection 32 of catheter shaft as depicted in the figures would passthrough roughly the center of the open circle formed by the third curvedsection 38 of catheter shaft. With the straight section 32 of cathetershaft approximately equally displaced from the outer peripheral wall 48of the third section 38 of catheter shaft, the straight section 32 ofcatheter shaft is less likely to press against the wall of, for example,a pulmonary vein that is being ablated during use of the ablationcatheter 18. This may be seen in, for example, FIG. 12, which depictsthe ablation catheter 18 in the left superior pulmonary vein 50 with thestraight section 32 of catheter shaft extending along the longitudinalaxis of the left superior pulmonary vein 50. Other curved sections couldbe used in place of the first curved section 34 of catheter shaft andthe second curved section 36 of catheter shaft if it were desired toplace the straight section 32 of catheter shaft in a different positionrelative to the third section 38 of catheter shaft, which contains theportholes that facilitate the formation of lesions.

[0049] As shown to good advantage in FIGS. 2-5, the portholes 40-44formed in the radial apex of the outer peripheral wall 48 of the thirdcurved section 38 of catheter shaft are circular and increase indiameter from the initial or first porthole 40 to the final or lastporthole 44. In other words, the porthole with the smallest diameter isthe initial porthole 40 and the porthole with the largest diameter isthe last porthole 44. Also in this embodiment, the distance 52 (see FIG.3 and compare 52′ of FIG. 6A) between the centers of adjacent portholesremains substantially constant. Thus, there is a bridge 54 betweenadjacent portholes, and the width of the bridges narrows as one movesfrom the first porthole 40 through the intermediate portholes 42 to thelast porthole 44. The bridge 54 spans the gap between, for example, thedistal trailing edge 56 of one porthole 40-44 and the proximal leadingedge 58 of the next adjacent porthole (see FIG. 7).

[0050] In the embodiment depicted in FIGS. 6 and 6A, the distal portion12 of the ablation catheter 18 of FIGS. 1-5 and 7 has essentially beenstraightened out to form a linear distal portion 12′. In other words,the complex curved configuration of the distal portion 12 depicted inFIGS. 1-5 and 7 is not present in the embodiment depicted in FIGS. 6 and6A. The specific embodiment of a distal portion 12′ depicted in FIGS. 6and 6A does, however, similarly have an active region including a firstporthole 40′, intermediate portholes 42′, and a last porthole 44′,wherein the relative diameter of the portholes 40′-44′ increases and thebridges 54′ between adjacent portholes decreases or narrows in size asone moves from the first porthole 40′ to the last porthole 44′. Also asclearly depicted in FIGS. 6 and 6A, the circular portholes 40′-44′ arecentered along a porthole centerline 60′, which is a tangent line on thesurface of the catheter shaft and extends parallel to the longitudinalaxis of the catheter shaft on the outer peripheral wall 48′ of thedistal portion 12′ of the ablation catheter. This is also true for theembodiment depicted in FIGS. 1-5 and 7, wherein the distal portion 12 iscurved. In other words, the portholes 40-44 depicted in FIGS. 1-5 and 7are also centered on a porthole centerline 60 (FIG. 5), which is alongitudinally extending tangent line on the radial apex of the outerperipheral wall 48 of the third curved section 38 of catheter shaft.

[0051] As alluded to above, the portholes permit a conductive fluidmedium 20, which contacts a metal electrode 16 (e.g., a platinum flatwire) embedded in the ablation catheter 18, to exit the distal portion12 of the ablation catheter 18 and contact adjacent tissue 14 to beablated. In the embodiment depicted in FIG. 7, a metal electrode 16 isconnected to an RF generator (not shown) by an electrical lead 62, whichextends down the catheter shaft 22 to the proximal portion 24 of thecatheter shaft 22 where it is connected to the RF generator in a knownmanner. In this embodiment, the metal electrode 16 emits RF energy 64(see FIG. 13), which exits the portholes to the adjacent tissue. Theembodiment depicted in FIGS. 1-5 and 7 also preferably includes a shapememory wire 66 (e.g., a flat wire comprising an alloy of nickel andtitanium, known commercially as NiTi wire or Nitinol wire), which helpsthe distal portion 12 of the ablation catheter 18 maintain a desiredconfiguration.

[0052] “Shape memory wire” as used herein means a strip of material(e.g., a circular or flat wire) which has the property that afterdeformation it will return to its former shape when heated to a certaintransition temperature. Thus, “shape memory wire” is wire that has beendeformed to a desired shape and briefly heated to “fix” that shape. Thewire possesses a “memory” causing it to return to its fixed shape afterbeing deformed. In the present invention, the shape memory wire 66 helpsa distal portion 12 of the ablation catheter 18 take and hold a desiredprofile or shape. Alternatively, the shape memory wire 66 could comprisea strip of stainless steel or another resilient metal, or it couldcomprise a plastic material.

[0053] In the embodiment depicted in FIGS. 1-5 and 7, the portholes40-44 are formed through the radial apex of the outer peripheral wall 48of the third curved section 38 of catheter shaft, and the shape memorywire 66 is located within the ablation catheter 18 adjacent to the innerperipheral wall 68 of the distal portion 12. A rounded tip 70 maycomprise the most distal end of the ablation catheter 18, and this tip70 may be a tip electrode. If a tip electrode is present at the mostdistal end of the ablation catheter 18, it may receive energy fromeither the same lead 62 that is connected to the metal electrode 16, ora second lead (not shown) may be inserted along the ablation catheter toseparately power the tip electrode.

[0054]FIG. 8 is a cross-sectional view along line 8-8 of FIG. 7 andshows further details concerning the internal configuration of theablation catheter 18 depicted in FIG. 7. It is apparent from FIG. 8 thatthis variant of the ablation catheter 18 includes a bi-lumenal cathetershaft. The bi-lumenal shaft in this variant includes a first lumen 72,which has a modified keyhole shape comprising a nearly-circularsubportion 74 mated with a rounded-rectangular subportion 76. Thesesubportions 74, 76 of the first lumen 72 are joined at a necked downarea 78 defining a pair of retention ledges 80, 82. In this embodiment,these retention ledges 80, 82 retain the metal electrode 16 in therounded-rectangular subportion 76 of the first lumen 72. Thenearly-circular subportion 74 of the first lumen 72 carries a conductivefluid medium 20 (see FIG. 13), which, by design, flows past, and incontact with, the metal electrode 16. A number of portholes 42 arevisible in FIG. 8 through the radial apex of the outer peripheral wall48 of the distal portion 12. A second lumen 84 depicted in cross-sectionin FIG. 8 carries the shape memory wire 66 (e.g., a NiTi flat wire)adjacent to the inner peripheral wall 68 of the distal portion 12. Inthis particular embodiment, the shape memory wire 66 does not directlycontact the conductive fluid medium 20 flowing into the patient'sbloodstream. Thus, it would be possible to use a shape memory wire 66constructed from any material without regard to that material'sbiocompatibility.

[0055]FIG. 9 depicts another possible cross-sectional configuration forthe ablation catheter. In this embodiment, only a first lumen 72′ ispresent. FIG. 9 also depicts a mere slice of the ablation catheter and,thus, only a single intermediate porthole 42′ through the radial apex ofthe outer peripheral wall 48′ is visible in FIG. 9. Similar to what isdepicted in FIG. 8, the first lumen 72′ depicted in FIG. 9 has amodified keyhole shape, comprising a nearly-circular subportion 74′mated with a rounded-rectangular subportion 76′ adjacent to innerperipheral wall 68′. In this embodiment, a metal electrode (not shown inFIG. 9) would be retained in the rounded-rectangular subportion 76′ ofthe first lumen 72′ by retention ledges 80′, 82′ at necked down area78′, and would provide both the energy for the ablation procedure aswell as the shape stability. For example, a NiTi flat wire could beplaced in the rounded-rectangular subportion 76′ of the first lumen 72′to serve as both the electrode and to provide configuration stability.If desired, the NiTi flat wire could be coated with a more conductivematerial (e.g., platinum, which is biocompatible with blood).

[0056]FIG. 10 depicts an alternative embodiment for the distal portion12″ of an ablation catheter according to the present invention. Thisembodiment is most similar to the embodiment depicted in FIG. 5, but athird curved section 38″ includes two rows 86 of portholes. In thissecond embodiment, each porthole has a corresponding porthole on theopposite side of the longitudinally-extending, circumferential tangentline 88 shown in this figure as bisecting the two rows 86 of portholes.The portholes could be staggered rather than side-by-side. This two rowembodiment would provide a wider lesion than the lesion provided by thedistal portion 12 depicted in FIG. 5, but would require acorrespondingly greater amount of energy to produce a sufficient lesionin the tissue being ablated.

[0057] FIGS. 11-14 depict the ablation catheter according to the presentinvention while being used to ablate tissue in a left superior pulmonaryvein 50. FIGS. 11 and 12 include a number of primary components of theheart to orient the reader. In particular, starting in the upperleft-hand portion of FIGS. 11 and 12, and working around the peripheryof the heart 30 in a counterclockwise fashion, the following parts ofthe heart 30 are depicted: superior vena cava 92, right atrium 94,inferior vena cava 96, right ventricle 98, left ventricle 100, leftinferior pulmonary vein 102, left superior pulmonary vein 50, leftatrium 104, right superior pulmonary vein 106, right inferior pulmonaryvein 108, left pulmonary artery 110, arch of aorta 112, and rightpulmonary artery 114. The distal portion 12 of the ablation catheter 18is positioned adjacent to the ostium 116 of the left superior pulmonaryvein 50 using known procedures like the “Seldinger technique.” Forexample, to get the distal portion 12 of the ablation catheter 18 in theposition shown in FIG. 11, the right venous system may be first accessedusing the “Seldinger technique,” wherein a peripheral vein (such as afemoral vein) is punctured with a needle, the puncture wound is dilatedwith a dilator to a size sufficient to accommodate an introducer (e.g.,28). The introducer (e.g., 28) with at least one hemostatic valve (seeFIG. 1) is seated within the dilated puncture wound while maintainingrelative hemostasis. With the introducer in place, the ablation catheter18 is introduced through the hemostatic valve of the introducer and isadvanced along the peripheral vein, into the region of the vena cava(e.g., the interior vena cava 96), and into the right atrium 94. Fromthere, the ablation catheter 18 together with the guiding introducer ortranseptal sheath is further advanced through a hole in the interatrialseptum, which a doctor would make before inserting the ablation catheter18 into the introducer, and into the left atrium. Once the ablationcatheter 18 is in the left atrium, it can be advanced to the respectivepositions depicted in FIGS. 11 and 12.

[0058] In FIG. 12, the distal portion 12 of the ablation catheter 18 hasbeen inserted into the left superior pulmonary vein 50. While theablation catheter 18 is in the pulmonary vein as depicted in FIG. 12,the electrode would be activated to create the desired lesion in theleft superior pulmonary vein 50. As shown in FIG. 13, the RF electriccurrent 64 emanating from the metal electrode 16 passes through theconductive fluid medium 20 contained in the nearly-circular subportion74 of the first lumen 72 through the portholes 42 and into the adjacenttissue 14. The conductive fluid medium 20 experiences ohmic heating asit flows along the metal electrode 16 and out the portholes 42. Thus, alesion is formed in the tissue 14 by the RF energy 64. Lesion formationmay also be facilitated by the conductive fluid medium 20, which mayhave been heated by ohmic heating to a sufficiently high temperature tofacilitate or enhance lesion formation, flowing out the portholes. TheRF energy is conducted into the adjacent tissue and the heatedconductive fluid medium convectively affects the temperature of thetissue. In order to form a sufficient lesion, it is desirable to raisethe temperature of the tissue to at least 50° C. for an appropriatelength of time (e.g., one minute). Thus, sufficient RF energy must besupplied to the metal electrode to produce this lesion-formingtemperature in the adjacent tissue for the desired duration.

[0059] The conductive fluid medium 20 flowing through the portholes40-44 prevents blood from flowing into the ablation catheter 18 andpushes blood from the area adjacent to the portholes 40-44. This helpsprevent coagulum, which can have undesirable effects on the patient. Theconductive fluid medium is caused to flow at a rate that prevents theelectrode from overheating the conductive fluid medium and producingvapor in the first lumen 72. If the conductive fluid medium were toboil, creating a vapor, the ablation catheter's ability to form adesired lesion in adjacent tissue 14 would be reduced or destroyed sincethe RF energy would be unable to/reach the tissue in sufficientquantity. Thus, the flow of conductive fluid medium through the firstlumen and out the portholes is managed or regulated so that there issufficient flow to prevent vaporization, but not so much flow that themetal electrode is prohibited from sufficiently heating the adjacenttissue to form a desired lesion. Also, if too much conductive fluidmedium flows out of the portholes, the hemodynamics of the patient maybe adversely affected by the excess quantity of conductive fluid mediumbeing mixed with the patient's blood. The desired flow rate is achievedby, for example, adjusting the pressure driving the conductive fluidmedium through the first lumen, changing the diameter or distribution ofthe portholes, altering the spacing between the portholes, and changingthe porthole diameter gradient between the small first porthole and therelatively larger last porthole. Another factor that may be taken intoaccount when adjusting the flow rate of the conductive fluid medium isthe specific configuration of the distal portion of the ablationcatheter since the flow of conductive fluid medium is affected by thecurvature of the catheter shaft.

[0060] In the alternative embodiment of a distal portion 12′″ depictedin FIG. 14, the portholes 40-44 depicted in, for example, FIG. 2 havebeen moved from the longitudinally-extending tangent line 60 (FIG. 5) onthe radial apex of the outer peripheral wall 48 of the third curvedsection 38 of catheter shaft to a distally-facing surface 118 at thedistal apex of a third curved section 38′″. In this configuration, thelongitudinal axes of the portholes extend parallel to the longitudinalaxis 46 (see FIGS. 2, 3, and 5) of the straight section 32 of cathetershaft 22, rather than extending radially outwardly from thatlongitudinal axis of the straight section of catheter shaft as is thecase with the embodiment of FIGS. 2-5 and 7. As with the embodimentsdescribed above, the longitudinal axis 46 of the straight section 32 ofcatheter shaft is substantially aligned with a longitudinal axis of apulmonary vein (e.g., 50 in FIG. 14). When the configuration depicted inFIG. 14 is used for pulmonary vein ablation, it is unnecessary to insertthe distal portion 12′″ of the ablation catheter into the pulmonary vein(compare FIG. 12, wherein the distal portion 12 has been inserted intothe left superior pulmonary vein 50). Rather, as shown in FIG. 14, thedistal portion of the ablation catheter is placed at the ostium 116 ofthe pulmonary vein 50 so that the third curved section 38′″ of cathetershaft substantially encircles the extended longitudinal axis (not shown)of the pulmonary vein 50. If RF energy is then applied to the ablationcatheter, a circular lesion is formed in the left atrium 104 at theostium 116 of the pulmonary vein 50, thereby inhibiting entry of strayelectrical signals from the pulmonary vein 50 into the left atrium 104.

[0061] Although preferred embodiments of this invention have beendescribed above with a certain degree of particularity, those skilled inthe art could make numerous alterations to the disclosed embodimentswithout departing from the spirit or scope of this invention. Forexample, the portholes 40-44 are shown at the radial apex of the outerperipheral wall 48 of the third curved section 38 in the embodiment ofFIGS. 2-5 and 7, and the portholes 40′″-42′″ are shown at the distalapex of the third curved section 38′″ in the embodiment of FIG. 14. Theportholes could, however, pass through the outer peripheral wall of thethird curved section at a location between the radial apex and thedistal apex. Further, all directional references (e.g., upper, lower,upward, downward, left, right, leftward, rightward, top, bottom, above,below, vertical, horizontal, clockwise, and counterclockwise) are onlyused for identification purposes to aid the reader's understanding ofthe present invention, and do not create limitations, particularly as tothe position, orientation, or use of the invention. It is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative only and notlimiting. Changes in detail or structure may be made without departingfrom the spirit of the invention as defined in the appended claims.

We claim:
 1. An ablation catheter for ablating tissue, the ablationcatheter comprising a catheter shaft, said catheter shaft comprising aproximal portion; a distal portion, said distal portion being adapted tobe inserted into a body cavity having tissue to be ablated and beingdisposed remotely from said proximal portion, said distal portioncomprising an active region including a plurality of portholes; and afirst lumen extend from said proximal portion to said distal portion,said first lumen being adapted to carry a conductive fluid medium fromsaid proximal portion to said portholes along said active region of saiddistal portion; and 1 a metal electrode mounted within said first lumenand extending along said active region of said distal portion, whereinsaid metal electrode is adapted to supply ablation energy to theconductive fluid medium.
 2. The ablation catheter of claim 1, whereinsaid conductive fluid medium is hypertonic saline.
 3. The ablationcatheter of claim 1, wherein said distal portion is straight.
 4. Theablation catheter of claim 3, wherein said straight distal portioncomprises a first porthole, at least one intermediate porthole, and alast porthole, and wherein said portholes are circular in cross section,and the relative diameter of said portholes increases in size as onemoves from said first porthole to said last porthole.
 5. The ablationcatheter of claim 4, wherein each of said portholes defines a proximalleading edge and a distal trailing edge, and wherein a bridge is definedbetween a proximal leading edge of one porthole and a distal trailingedge of a next adjacent porthole, and wherein said bridges betweenadjacent portholes decrease in size as one moves from said firstporthole to said last porthole.
 6. The ablation catheter of claim 4,wherein said portholes are centered along a porthole centerline definedby a tangent line on a surface of said catheter shaft extending parallelto a longitudinal axis of said catheter shaft on an outer peripheralwall of said distal portion of said ablation catheter.
 7. The ablationcatheter of claim 1, wherein said distal portion of said catheter shaftincludes a first curved section, a second curved section, and a thirdcurved section.
 8. The ablation catheter of claim 1, wherein said distalportion of said catheter shaft includes at least one curved section. 9.The ablation catheter of claim 8, wherein said at least one curvedsection of said catheter shaft includes said plurality of portholesthrough which the conductive fluid medium is adapted to flow.
 10. Theablation catheter of claim 9, wherein said plurality of portholesincludes a first porthole, a plurality of intermediate portholes, and alast porthole.
 11. The ablation catheter of claim 10, wherein said atleast one curved section is shaped in a circular configuration.
 12. Theablation catheter of claim 11, wherein said curved section defines anouter peripheral wall, and wherein said portholes extend from said firstlumen through a radial apex of said outer peripheral wall.
 13. Theablation catheter of claim 12, wherein each of said portholes has acircular cross section, and wherein said first porthole has a diameterthat is smaller than the diameters of each of the other portholes, andwherein said last porthole has a diameter that is larger than thediameters of each of the other portholes, and further where thediameters of the portholes increase in size from said first porthole tosaid last porthole.
 14. The ablation catheter of claim 13, wherein eachof said portholes is sized so that the conductive fluid medium isadapted to flow evenly from each of said portholes.
 15. The ablationcatheter of claim 13, wherein each of said portholes defines a proximalleading edge and a distal trailing edge, and wherein a bridge is definedbetween a proximal leading edge of one porthole and a distal trailingedge of a next adjacent porthole.
 16. The ablation catheter of claim 15,wherein each of said bridges has a width, and wherein said width of saidbridges narrows from said first porthole to said last porthole.
 17. Theablation catheter of claim 15, wherein each of said portholes has alongitudinal centerline, and wherein a distance between saidlongitudinal centerlines of adjacent portholes remains constant alongsaid active region.
 18. The ablation catheter of claim 13, wherein eachporthole is separated from at least one next adjacent porthole by abridge extending between edges of said adjacent portholes.
 19. Theablation catheter of claim 13, wherein said portholes are centered on aporthole centerline defined by a longitudinally-extending tangent lineon a surface of said catheter shaft on said radial apex of said outerperipheral wall of said at least one curved section.
 20. The ablationcatheter of claim 1, wherein said metal electrode is a platinum flatwire adapted to be connected to an RF generator by an electrical leadthat extends from said distal portion to said proximal portion of saidcatheter shaft.
 21. The ablation catheter of claim 1, wherein saidablation catheter further comprises a shape memory wire.
 22. Theablation catheter of claim 21, wherein said catheter shaft furthercomprises a second lumen extending along said distal portion adjacent toan inner peripheral wall of said distal portion, and wherein said shapememory wire is located within said second lumen.
 23. The ablationcatheter of claim 22, wherein said shape memory wire comprises an alloyof nickel and titanium.
 24. The ablation catheter of claim 22, whereinsaid shape memory wire comprises a strip of stainless steel.
 25. Theablation catheter of claim 1, wherein said distal portion furthercomprises a tip electrode.
 26. The ablation catheter of claim 1, whereinsaid catheter shaft is bi-lumenal, including a first lumen and a secondlumen.
 27. The ablation catheter of claim 26, wherein said first lumenhas a modified keyhole shape, comprising a nearly-circular subportionmated with a rounded-rectangular subportion.
 28. The ablation catheterof claim 27, wherein said nearly-circular subportion mates with saidrounded-rectangular subportion at a necked down area defining a pair ofretention ledges.
 29. The ablation catheter of claim 28, wherein saidretention ledges retain said metal electrode in said rounded-rectangularsubportion of said first lumen.
 30. The ablation catheter of claim 28,wherein said nearly-circular subportion of said first lumen is adaptedto carry the conductive fluid medium flowing past and in contact withsaid metal electrode.
 31. The ablation catheter of claim 28, whereinsaid second lumen carries said shape memory wire.
 32. The ablationcatheter of claim 26, wherein said distal portion defines an innerperipheral wall and an outer peripheral wall, and wherein said firstlumen is adjacent to said outer peripheral wall and said second lumen isadjacent to said inner peripheral wall.
 33. The ablation catheter ofclaim 32, wherein said first lumen further comprises a modified keyholeshape defined by a nearly-circular subportion mated with arounded-rectangular subportion.
 34. The ablation catheter of claim 33,wherein retention ledges are defined at a necked down area between saidnearly-circular subportion and said rounded-rectangular subportion ofsaid first lumen, and wherein said retention ledges retain said metalelectrode in said rounded-rectangular subportion of said first lumen.35. An ablation catheter for ablating tissue, the ablation cathetercomprising a catheter shaft, said catheter shaft comprising a proximalportion; a distal portion comprising at least one curved section adaptedto be inserted into a body cavity having tissue to be ablated, whereinsaid at least one curved section defines an inner peripheral wall and anouter peripheral wall, and wherein said outer peripheral wall has anactive region that includes a plurality of portholes; a first lumenextending from said proximal portion to said distal portion, said firstlumen being adapted to carry a conductive fluid medium from saidproximal portion to said portholes along said active region of saiddistal portion; and a second lumen extending adjacent to said innerperipheral wall; a metal electrode mounted in said first lumen andextending along said active region of said distal portion, wherein saidmetal electrode is adapted to supply ablation energy to the conductivefluid medium; and a shape memory wire mounted in said second lumen. 36.An ablation catheter assembly for treatment of cardiac arrhythmia, theablation catheter assembly comprising an ablation catheter according toclaim 1 or 35; and at least one guiding introducer.
 37. The ablationcatheter assembly of claim 36, wherein said at least one guidingintroducer comprises an inner guiding introducer and an outer guidingintroducer.
 38. An ablation catheter assembly for treatment of cardiacarrhythmia, the ablation catheter assembly comprising an ablationcatheter according to claim 1 or 35; and a precurved sheath.
 39. Amethod for making a catheter assembly for treating cardiac arrhythmia,the method comprising the steps of acquiring a shape memory wire havinga desired curvilinear shape; acquiring a catheter shaft having a firstlumen formed therein; inserting said shape memory wire into said firstlumen to form a catheter assembly; heating said catheter shaft until itrelaxes and at least partially conforms to said shape of said shapememory wire; and cooling said catheter assembly.
 40. The method of claim39, wherein said heating step includes heating said catheter assembly toa temperature that permits said catheter shaft to deform, and whereinsaid temperature remains lower than a temperature used to fix said shapeof said shape memory wire.
 41. The method of claim 40, wherein a portionof said catheter shaft over said shape memory wire includes a pluralityof portholes.
 42. The method of claim 39, wherein said shape memory wirecomprises an alloy of nickel and titanium.
 43. The method of claim 42,wherein said memory wire comprises NiTi.